1. Field of the Invention
The present invention relates to a gas turbine apparatus, and more particularly to a gas turbine apparatus used in a micro-gas turbine power generating system or the like. The present invention also relates to a gas turbine power generating system employing such a gas turbine apparatus to generate electric power.
2. Description of the Related Art
For example, a digestion gas mainly containing methane is produced in a digestion process of biomass, and a pyrolysis gas mainly containing carbon monoxide, hydrogen, and hydrocarbon is produced in a gasification process of biomass. Such gases have a small heating value per unit volume. While a town gas has a lower heating value of about 50,233 kJ/kg (12,000 kcal/kg), a digestion gas has a lower heating value of about 25,116 kJ/kg (6,000 kcal/kg), which is a half of the lower heating value of the town gas. A pyrolysis gas has a lower heating value of about 5,023 kJ/kg (1,200 kcal/kg), which is a tenth of the lower heating value of the town gas.
Ratios of combustible components vary in gases having a small heating value, which are produced from biomass, according to places, seasons, or time. The heating values of these gases are accordingly changed. Generally, as the lower heating value of a fuel gas is smaller, the fuel gas is less likely to be ignited and to be stably combusted. Particularly, gases having a lower heating value smaller than about 6,279 kJ/kg (1,500 kcal/kg) have difficulty in maintaining combustion in a heat engine such as a gas turbine or a gas engine.
Accordingly, as a fuel gas has a smaller heating value, it is more difficult to ignite the fuel gas in a heat engine such as a gas turbine or a gas engine and start the heat engine reliably. Particularly, in a gas turbine apparatus having a recuperator, a combustion temperature is slowly increased at the beginning of operation because the recuperator has a large heat capacity. Accordingly, it is difficult to reliably start the gas turbine apparatus with use of a gas having a small heating value.
Recently, the following attempts have been made to utilize a gas having a small heating value in a heat engine such as a gas turbine or a gas engine. A gas having a small heating value is refined to a high degree to increase its heating value. Alternatively, a gas having a small heating value is mixed with a fuel gas having a large heating value such as a propane gas. However, these systems have a poor investment efficiency and have not widely spread. Accordingly, most of a digestion gas and a pyrolysis gas are incinerated in practical use even though they have a relatively large heating value.